The present invention pertains to an improved fluid drop detection method and apparatus. More particularly, the present invention is directed to a method and apparatus for detecting drops over a period of time and comparing the current drop time period to limits defined by previous drops.
The invention is contemplated specifically for use in the administration of parenteral solutions to patients in hospitals and the like, but it also can be utilized for detecting and controlling drop flow of any liquid in precise quantities over a desired period of time into chemical or biological reactors, industrial processes, and the like.
While the administration of parenteral solutions is a common practice in hospitals, and great quantities of equipment of many different types are sold for the purpose of providing such administration, in many instances the medical situation calls for the administration of precisely controlled amounts of medication on a continuous drip basis over a period which may last several days or weeks. Cancer chemotherapy agents, for example, may be administered in this manner.
For these agents, and for many other medications, they must, of course be administered to the patient in sufficient quantities to be effective, and often a uniform, continuous low volume dose is required. At the same time, an accidental increase in the flow rate can be life threatening in the case of some medications, and thus totally must be avoided.
The drop flow from conventional, gravity-operated parenteral solution equipment is subject to a wide range of variable situations, such as fluid viscosities, tubing properties and resonant phenomenon. These and other effects can cause intermittent drop flow.
In the prior art, numerous patents exist which suggest various systems for controlling the flow of parenteral solution through a large assortment of electronic devices which purportedly provide improved flow accuracy. As a typical example of such prior art, drops of the solution are formed and fall through a conventional drip chamber in an administration set and are detected as they fall by a drop detector which can operate on photometric principles, by sensing variations in capacitance, or the like. A flow control clamp valve or other occlusion device is provided in the flow conduit and is controlled by a feedback mechanism, typically electronic, for sensing the drop rate in the drip chamber and appropriately controlling the valve so that the drop rate is kept within desired parameters.
In the prior art, a pump often is used to propel the solution through the set. This carries its own hierarchy of risks, and requires the presence of safety systems to prevent the pumping of air into the patient in the event that the source of parenteral solution runs dry. Such safety systems are, of course, subject to breakdown and failure, and the consequences of that also potentially are fatal.
It therefore is preferable, for safety and simplicity, to utilize a gravity operated system which precisely measures amounts of parenteral solution to a patient. One such system is disclosed and claimed in co-pending U.S. Application Ser. No. 336,154, filed Jan. 6, 1982, in the name of Rene Lamadrid for MOTOR DRIVEN OCCLUSION CONTROLLER FOR LIQUID INFUSION AND THE LIKE, which application is assigned to the assignee of the present invention and is incorporated herein by reference.
As disclosed therein, an integral part of the system is a drop detector which detects drops as they pass through a drip chamber. In this system a fixed drop rate is selected and the actual drop rate is compared thereto to provide a control signal to the occlusion controller. The precision of the drop detection is critical in this type of system.